The invention relates to zigzag sewing machines in general and more particularly relates to a pattern cam driving mechanism of the zigzag sewing machine, in which a first group of pattern cams is rotated in association with the rotation of a drive shaft of the sewing machine with a reduced speed and a second group of pattern cams is rotated in association with the rotation of the first group of pattern cams with a further reduced speed with a transmission mechanism having a predetermined speed reduction ratio and provided between the first and second groups of pattern cams.
Generally a sewing machine has a standardized size and accordingly the space within the machine housing is limited. Especially in a zigzag sewing machine of the type having a number of pattern cams incorporated or separately provided as being exchangeable, in any case, to cooperate with a cam follower which is swingable in accordance with the contours of the pattern cams, the diameter of the pattern cams has been accordingly limited resulting in the limitation in the number of stitches produced in one rotation cycle of the pattern cams and therefore the variation of stitched patterns has been limited.